Optical comb frequency interval multiplication device and implementation method thereof

Abstract

The present invention discloses an optical comb frequency interval multiplication device and its implementation method. The device comprises an optical frequency comb, a beam splitter, a vacuum chamber, and multiple interval multiplication branches. Each interval multiplication branch comprises a first polarization beam splitter, an FP cavity, a broadband Faraday rotator, a half-wave plate, a second polarization beam splitter, a broadband Faraday isolator, and first and second reflectors. The device cleverly utilizes the broadband Faraday rotator and the half-wave plate to re-introduce the spectrum, which has undergone frequency multiplication after a first pass through the FP cavity, into the same FP cavity, doubling the side mode suppression ratio while avoiding inter-stage oscillation and collinear interference. The device can achieve long-term stable frequency interval multiplication. The resulting calibration spectrum can be used for planetary mass measurement, dark matter discovery, precision ranging, low-noise microwave generation, and high-speed analog-to-digital conversion. The overall system structure of the device is simple, and the adjustment method is simple.

Description

Technical Field

[0001] The present invention relates to optical frequency comb technology, and in particular to an optical comb frequency interval multiplication device and an implementation method thereof. Background Art

[0002] As high-resolution spectroscopy places increasing demands on calibration technology, femtosecond laser frequency combs, with their uniformly spaced spectral lines and uniform frequency spacing, are considered a new generation of calibration sources. However, conventional mode-locked lasers used to generate laser frequency combs struggle to achieve frequency spacings exceeding 1 GHz.

[0003] Lasers with frequency spacing above 1 GHz suffer from pulse widths, low pulse energy, and difficulty in direct spectrum expansion, requiring complex amplification, compression, and even pulse shaping. Microcavity optical combs, while capable of frequency spacings of tens or even hundreds of GHz, have wavelengths concentrated within a spectral range centered around 1.5 microns, making them unsuitable for use in the visible light band. They also require complex startup procedures, suffer from low power, wide pulse widths, wide variations in spectral intensity distribution, and poor thermal stability, making them difficult to use for astronomical spectral calibration.

[0004] Femtosecond optical frequency combs commercially used in astronomical spectrometers have a single frequency interval and a wavelength range exceeding 500 nm. This makes them unsuitable for the short-wavelength resolution of spectrometers. They also suffer from limited coverage, large size, high cost, and complex system operation. Therefore, a simple, reliable calibration device suitable for high-resolution spectrometers in harsh environments is urgently needed.

[0005] The calibration light source used for astronomical spectral calibration consists of a series of resolvable optical frequency standards. A series of resolvable light spots are visible above the spectrum. The size of these light spots is a function of the diffraction spot fit. If this optical frequency standard is filtered using a dense optical frequency standard, the size and symmetry of the filtered side modes determine the accuracy of the calibration. Based on the error formula for the radial velocity (RV) of these filtered optical frequency standards, astronomical spectral calibration requires a very high side mode suppression ratio and symmetry. This formula is:

[0006]

[0007] Among them, f R is the comb tooth spacing of the laser frequency comb; f A is the optical frequency of the calibrated comb teeth after multiplication, c is the speed of light in vacuum, I +1 and I -1 are the two side modes adjacent to the main mode I0 under the FP cavity envelope. Formula (1) shows that (I +1 -I -1 ) / I0 is the ratio of the main mode I0 under the FP cavity envelope, especially the difference between them plays a crucial role in the error of the radial velocity.+1 -I -1 ≠0, (I +1 -I -1 ) / I0 should be as small as possible, that is, the side mode suppression ratio should be as high as possible.

[0008] Therefore, spectral filtering must first be symmetrical, that is, the resonant frequency (or extinction range) of the FP cavity used for filtering is an integer multiple of the optical frequency comb. Frequency multiplication is performed by the FP cavity. The calculation formula for the side mode suppression ratio S (the ratio of the main mode to the side mode under the transmission linewidth) is expressed in dB as:

[0009]

[0010] Where F is the finesse of the FP cavity, and M is the frequency multiplication factor. If the reflectivity of the FP cavity's mirrors is 99% and the frequency multiplication factor is M = 30, then F = 312. This results in a side-mode suppression ratio (S) of only 26 dB, which does not meet the requirement of greater than 30 dB. Therefore, two or more passes through the FP cavity are necessary.

[0011] Although the cascaded FP cavity can solve the problem of side mode suppression, when two or more FP cavities are cascaded, the light output from the first FP cavity will oscillate between the two FP cavities, resulting in the first-stage multiplied spectrum not being able to completely pass through the second FP cavity, or the spectrum being severely modulated.

[0012] Furthermore, the two FP cavities required for cascading must have exactly the same frequency spacing. If the FP cavity is actively stabilized (driven by a PZT), cascading is not a problem. However, actively stabilized FP cavities require optical locking with continuous light, which is then frequency-shifted as a reference light. The reference light is then used to lock the FP cavity using the reflectance differential locking method (PDH). This system is complex and has poor long-term stability.

[0013] Passively stabilized FP cavities use ultra-low expansion (ULE) glass as spacers and have no moving parts. As long as the temperature is stable, the FP cavity can remain stable for a long time. However, creating two identical FP cavities is difficult in practice. The best approach is to re-pass the light that first passed through the FP cavity through the same FP cavity. This approach presents the following problems:

[0014] If the light passing through the first FP cavity is returned to the first FP cavity through a Faraday rotator and a half-wavelength plate, although the reflection and oscillation on the surfaces of the two FP cavities can be isolated, the reflected light will be mixed into the final output light, causing the second filtering to fail. Summary of the Invention

[0015] In order to solve the problem of insufficient side mode suppression ratio of a single-pass FP cavity and inaccurate spectrum calibration, the present invention proposes an optical comb frequency interval multiplication device and an implementation method thereof.

[0016] One object of the present invention is to provide an optical comb frequency interval multiplication device.

[0017] The optical comb frequency interval multiplication device of the present invention comprises: an optical frequency comb, a light splitter, a vacuum chamber and multiple interval multiplication branches;

[0018] A plurality of light entrance windows are provided on one side of the vacuum chamber, corresponding to each light entrance window, and a plurality of light exit windows are provided on the other side opposite the vacuum chamber; a multi-path spaced multiplication branch is located in the vacuum chamber, and each spaced multiplication branch corresponds to a pair of corresponding light entrance windows and light exit windows; each spaced multiplication branch includes: a first polarization beam splitter, a Fabry-Perot (FP) cavity, a broadband Faraday rotator, a half-wave plate, a second polarization beam splitter, a broadband Faraday isolator, and first and second reflectors, wherein the optical axes of the first polarization beam splitter, the FP cavity, the broadband Faraday rotator, the half-wave plate, and the second polarization beam splitter, which are sequentially arranged along a horizontal line, are coaxial with the corresponding light entrance window and light exit window;

[0019] The optical frequency comb emits a broadband optical comb spectrum, and the polarization state of the optical comb spectrum is adjusted to horizontal polarization; the broadband optical comb spectrum is divided into multiple paths according to wavelength by the optical splitter, and one wavelength band corresponds to an interval multiplication branch; the horizontally polarized light enters the vacuum chamber through the corresponding vacuum chamber light entrance window, and is incident on the first polarization beam splitter; the horizontally polarized light passes through the first polarization beam splitter and is transmitted to the FP cavity of the corresponding wavelength band; the frequency interval is set by adjusting the cavity length of the FP cavity to perform frequency multiplication, and the required frequency, i.e., the comb tooth, is selected. The comb spectrum is first transmitted to the broadband Faraday rotator and half-wave plate; the polarization state is converted from horizontal polarization to vertical polarization by the broadband Faraday rotator and half-wave plate, and then transmitted to the second polarization beam splitter; the vertically polarized light returned from the incident surface of the FP cavity is reflected by the first polarization beam splitter to the second reflector; the vertically polarized light transmitted from the output surface of the FP cavity is reflected by the second polarization beam splitter, and then reflected by the first reflector to the broadband Faraday isolator, and the vertically polarized light returned from the incident surface of the FP cavity is transmitted to the second reflector. The vertical polarized light passing through the FP cavity's exit surface is isolated by a broadband Faraday isolator to prevent the vertically polarized light reflected from the incident surface of the FP cavity from returning to the exit surface of the FP cavity, thereby preventing the reflected light from the incident surface of the FP cavity from mixing with the signal light passing through the second time. The vertically polarized light passing through the exit surface of the FP cavity is reflected by the second reflector via the broadband Faraday isolator and transmitted to the first polarization beam splitter. The vertically polarized light is reflected by the first polarization beam splitter and transmitted to the same FP cavity again, where it undergoes a second filtering through the same FP cavity, thereby achieving multiple filtering using one FP cavity to improve the side mode suppression ratio. The vertically polarized light comb spectrum passing through the FP cavity for the second time is restored to horizontally polarized light by a broadband Faraday rotator and a half-wave plate. The broadband Faraday rotator and the half-wave plate make the polarization states of the light comb spectrum passing through the FP cavity for the first time and the light comb spectrum passing through the FP cavity for the second time perpendicular to each other, thereby distinguishing the light comb spectrum passing through the FP cavity for the first time from the light comb spectrum passing through the FP cavity for the second time. The parallel polarized light comb spectrum passing through the FP cavity for the second time is transmitted through the second polarization beam splitter and output as calibration light.

[0020] The FP cavity consists of two mirrors and a spacer. The first mirror is a plano-concave mirror with one flat surface and the other concave, with the concave surface facing inward. The second mirror has two flat surfaces, with a typical 30-degree angle between them to prevent sub-cavity effects. The inner surfaces of both mirrors are coated with a high-reflection coating for the wavelength range, while the other mirror is coated with an anti-reflection coating for the same wavelength range. A spacer with ventilation holes is placed between the two mirrors. The spacer spacing defines the distance between the two mirrors, which is the cavity length of the FP cavity. Both mirrors and the spacer are made of ultra-low expansion (ULE) glass. By adjusting the spacing between the two mirrors in the FP cavity, the frequency interval, or frequency multiplication factor, is set, allowing the desired frequency to be selected.

[0021] The vacuum chamber is made of stainless steel. The light entrance window and light exit window of the vacuum chamber are made of quartz glass. Both sides of the light entrance window and light exit window are coated with broadband anti-reflection film. The light entrance window and light exit window are fixed and sealed with the vacuum chamber with standard flanges. The vacuum chamber has an exhaust pipe, which is used to evacuate the vacuum chamber to a vacuum better than 10 -5 Pa, after evacuation, the vacuum chamber will be maintained by an ion pump.

[0022] Broadband Faraday rotators and broadband Faraday isolators use the magneto-optical material cerium trifluoride (CeF3), which has a wide transparency band in visible light.

[0023] Another object of the present invention is to provide a method for realizing an optical comb frequency interval multiplication device.

[0024] The method for implementing the optical comb frequency interval multiplication device of the present invention comprises the following steps:

[0025] 1) The optical frequency comb emits a broadband optical comb spectrum, and the polarization state of the optical comb spectrum is adjusted to horizontal polarization;

[0026] 2) The broadband optical comb spectrum is split into multiple paths according to wavelength by an optical splitter, with one wavelength segment corresponding to one interval multiplication branch;

[0027] 3) The horizontally polarized light enters the vacuum chamber through the corresponding light entrance window and is incident on the first polarization beam splitter;

[0028] The horizontally polarized light passes through the first polarization beam splitter and is transmitted to the FP cavity of the corresponding wavelength band;

[0029] 4) Frequency multiplication is performed by adjusting the FP cavity length to set the frequency interval, selecting the required frequency, i.e., the comb teeth. The frequency-multiplied optical comb spectrum is first transmitted to a broadband Faraday rotator and a half-wave plate;

[0030] 5) The polarization state is converted from horizontal polarization to vertical polarization through a broadband Faraday rotator and a half-wave plate, and transmitted to the second polarization beam splitter; the vertically polarized light returned from the incident surface of the FP cavity is reflected by the first polarization beam splitter to the second reflector;

[0031] 6) The vertically polarized light transmitted from the output surface of the FP cavity is reflected by the second polarization beam splitter and then reflected by the first reflector to the broadband Faraday isolator. The broadband Faraday isolator isolates the vertically polarized light returning from the incident surface of the FP cavity, preventing the vertically polarized light reflected from the incident surface of the FP cavity from returning to the output surface of the FP cavity, thereby preventing the reflected light from the incident surface of the FP cavity from mixing with the second transmitted signal light;

[0032] 7) The vertically polarized light transmitted from the output surface of the FP cavity is reflected by the second reflector through the broadband Faraday isolator and transmitted to the first polarization beam splitter;

[0033] 8) The vertically polarized light is reflected by the first polarization beam splitter and transmitted to the same FP cavity again, where it undergoes a second filtering, thus achieving multiple filtering using one FP cavity to increase the side mode suppression ratio.

[0034] 9) The vertically polarized light comb spectrum that passes through the FP cavity for the second time passes through a broadband Faraday rotator and a half-wave plate and is restored to horizontally polarized light. As a result, the broadband Faraday rotator and the half-wave plate make the polarization states of the light comb spectrum that passes through the FP cavity for the first time and the light comb spectrum that passes through the FP cavity for the second time perpendicular to each other, thereby distinguishing the light comb spectrum that passes through the FP cavity for the first time from the light comb spectrum that passes through the FP cavity for the second time. The parallel polarized light comb spectrum that passes through the FP cavity for the second time passes through the second polarization beam splitter and is output as calibration light.

[0035] In step 3), the vacuum chamber is evacuated to a temperature better than 10 -5 Pa.

[0036] In step 4), the FP cavity includes two cavity mirrors and a gasket, and the distance between the two cavity mirrors is defined by the gasket, that is, the cavity length of the FP cavity. Setting the frequency interval is setting the frequency multiplication multiple.

[0037] Advantages of the present invention:

[0038] The present invention cleverly utilizes a broadband Faraday rotator and a half-wave plate to re-introduce the frequency-doubled spectrum that has passed through the FP cavity for the first time into the same FP cavity, thereby doubling the side mode suppression ratio while avoiding inter-stage oscillation and collinear interference. It can achieve long-term stable frequency interval doubling. The generated calibration spectrum can be used for planetary mass measurement, dark matter discovery, precision ranging, low-noise microwave generation, high-speed analog-to-digital conversion, etc. The entire system structure of the present invention is simple, and the adjustment method is simple. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 A schematic diagram of an interval multiplication branch of an optical comb frequency interval multiplication device according to an embodiment of the present invention;

[0040] Figure 2 Schematic diagram of two interval multiplication branches of an embodiment of the optical comb frequency interval multiplication device of the present invention. DETAILED DESCRIPTION

[0041] The present invention will be further described below through specific embodiments in conjunction with the accompanying drawings.

[0042] like Figure 1 As shown, the optical comb frequency interval multiplication device of this embodiment includes: an optical frequency comb, a beam splitter, a vacuum chamber and two interval multiplication branches;

[0043] A plurality of light entrance windows are provided on one side of the vacuum chamber, corresponding to each light entrance window, and a plurality of light exit windows are provided on the other side opposite the vacuum chamber, corresponding to the outputs of the frequency multiplication branches of each wavelength; two spaced multiplication branches are located in the vacuum chamber, and each spaced multiplication branch corresponds to a pair of corresponding light entrance windows and light exit windows; each spaced multiplication branch includes: a first polarization beam splitter, a Fabry-Perot (FP) cavity, a broadband Faraday rotator, a half-wave plate, a second polarization beam splitter, a broadband Faraday isolator, and a first and a second reflector, all of which are located in the vacuum chamber, and the optical axes of the first polarization beam splitter, the FP cavity, the half-wave plate, and the second polarization beam splitter, which are arranged in sequence along a horizontal line, are coaxial with the corresponding light entrance window and light exit window.

[0044] The optical frequency comb emits a broadband optical comb spectrum with a frequency interval of 1GHz, and the polarization state of the optical comb spectrum is horizontal polarization; the broadband optical comb spectrum is divided into two paths according to the wavelength by the optical splitter, an optical comb spectrum with a wavelength of 560-900nm and an optical comb spectrum with a wavelength of 400-550nm, and the two wavelength bands correspond to one interval multiplication branch respectively; the horizontally polarized light enters the vacuum chamber through the corresponding vacuum chamber light entrance window, and is incident on the first polarization beam splitter; the horizontally polarized light passes through the first polarization beam splitter and is transmitted to the FP cavity; the frequency interval is set by adjusting the cavity length of the FP cavity, that is, the frequency multiplication is set. The frequency is multiplied by multiples of 1 / 4 to select the required frequency. One channel is multiplied by 30 times to 30 GHz, and the other channel is multiplied by 45 times to 45 GHz. The optical comb spectrum after frequency multiplication is first transmitted to the broadband Faraday rotator and half-wave plate; the polarization state is converted from horizontal polarization to vertical polarization by the broadband Faraday rotator and half-wave plate, and then transmitted to the second polarization beam splitter; the vertically polarized light returned from the incident surface of the FP cavity is reflected by the first polarization beam splitter to the second reflector; the vertically polarized light transmitted from the output surface of the FP cavity is reflected by the second polarization beam splitter, and then transmitted to the first reflector. The vertical polarized light reflected from the incident surface of the FP cavity is reflected by the second reflector to the broadband Faraday isolator, and the broadband Faraday isolator isolates the vertical polarized light returned from the incident surface of the FP cavity to prevent the vertical polarized light reflected from the incident surface of the FP cavity from returning to the exit surface of the FP cavity, thereby avoiding the reflection light of the incident surface of the FP cavity from mixing with the signal light transmitted for the second time; the vertical polarized light transmitted from the exit surface of the FP cavity is reflected by the second reflector through the broadband Faraday isolator and transmitted to the first polarization beam splitter; the vertical polarized light is reflected by the first polarization beam splitter and transmitted to the same FP cavity again, and is filtered for the second time through the same FP cavity , realizing multiple filtering using one FP cavity to improve the side mode suppression ratio; the vertically polarized light comb spectrum that passes through the FP cavity for the second time passes through a broadband Faraday rotator and a half-wave plate and is restored to horizontally polarized light, so that the polarization states of the light comb spectrum that passes through the FP cavity for the first time and the light comb spectrum that passes through the FP cavity for the second time are perpendicular to each other through the broadband Faraday rotator and the half-wave plate, thereby distinguishing the light comb spectrum that passes through the FP cavity for the first time from the light comb spectrum that passes through the FP cavity for the second time, and the parallel polarized light comb spectrum that passes through the FP cavity for the second time passes through the second polarization beam splitter and is output as calibration light.

[0045] The FP cavity consists of two mirrors and a gasket. The first mirror is a plano-concave mirror with one flat surface and the other concave, with the concave surface facing inward. The second mirror has two flat surfaces, with a certain angle (usually 30 minutes) between the two flat surfaces. The inner surfaces of the two plane mirrors are coated with a high-reflection film for the wavelength range, and the other surfaces are coated with an anti-reflection film for the wavelength range. The plane reflection of the first mirror serves as the incident surface of the FP cavity, while the outer plane mirror of the second mirror serves as the exit surface of the FP cavity. A gasket is placed between the two mirrors, with ventilation holes on the side of the gasket. The gasket spacing determines the distance between the two mirrors, that is, the cavity length of the FP cavity. Both the two mirrors and the gasket are made of ultra-low expansion (ULE) glass. The frequency interval is set by adjusting the spacing between the two mirrors of the FP cavity, and the required frequency is selected.

[0046] The vacuum chamber is made of stainless steel. The light entrance window and light exit window of the vacuum chamber are made of quartz glass. Both sides of each window are coated with broadband anti-reflection film. The light entrance window and light exit window are fixed and sealed with the vacuum chamber using standard flanges. The vacuum chamber has an exhaust pipe, which is used to evacuate the vacuum chamber to a vacuum better than 10 -5 Pa, after evacuation, the vacuum chamber will be maintained by an ion pump.

[0047] Broadband Faraday rotators and broadband Faraday isolators use the magneto-optical material cerium trifluoride CeF3, which has a wide transparency band in visible light.

[0048] The spectrometer uses a two-color filter.

[0049] Finally, it should be noted that the purpose of disclosing the embodiments is to facilitate a further understanding of the present invention. However, those skilled in the art will appreciate that various substitutions and modifications are possible without departing from the spirit and scope of the present invention and the appended claims. Therefore, the present invention should not be limited to the contents disclosed in the embodiments; the scope of protection claimed by the present invention shall be determined by the scope defined in the claims.

Claims

1. An optical comb frequency interval multiplication device, characterized in that: The optical comb frequency interval multiplication device comprises: an optical frequency comb, a beam splitter, a vacuum chamber and multiple interval multiplication branches; A plurality of light entrance windows are provided on one side of the vacuum chamber, corresponding to each light entrance window, and a plurality of light exit windows are provided on the other side opposite the vacuum chamber; a multi-path spaced multiplication branch is located in the vacuum chamber, and each spaced multiplication branch corresponds to a pair of corresponding light entrance windows and light exit windows; each spaced multiplication branch includes: a first polarization beam splitter, a Fabry-Perot FP cavity, a broadband Faraday rotator, a half-wave plate, a second polarization beam splitter, a broadband Faraday isolator, and first and second reflectors, wherein the optical axes of the first polarization beam splitter, the FP cavity, the broadband Faraday rotator, the half-wave plate, and the second polarization beam splitter, which are sequentially arranged along a horizontal line, are coaxial with the corresponding light entrance window and light exit window; The optical frequency comb emits a broadband optical comb spectrum, and the polarization state of the optical comb spectrum is adjusted to horizontal polarization. The broadband optical comb spectrum is divided into multiple paths according to wavelength by an optical splitter, with one wavelength band corresponding to an interval multiplication branch. The horizontally polarized light enters the vacuum chamber through the corresponding vacuum chamber entrance window and is incident on the first polarization beam splitter. The horizontally polarized light passes through the first polarization beam splitter and is transmitted to the FP cavity of the corresponding wavelength band. The frequency multiplication is performed by adjusting the cavity length of the FP cavity to set the frequency interval, and the required frequency, i.e., the comb tooth, is selected. The frequency-multiplied optical comb spectrum is first transmitted to a broadband Faraday rotator and a half-wave plate. The polarization state is converted from horizontal polarization to vertical polarization by the broadband Faraday rotator and the half-wave plate, and then transmitted to the second polarization beam splitter. The vertically polarized light returning from the incident surface of the FP cavity is reflected by the first polarization beam splitter to the second reflector. The vertically polarized light passing through the output surface of the FP cavity is reflected by the second polarization beam splitter and then reflected by the first reflector to the broadband Faraday isolator. The vertically polarized light returning from the incident surface of the FP cavity is then transmitted by the broadband Faraday isolator. Isolation is performed to prevent the vertically polarized light reflected from the incident surface of the FP cavity from returning to the exit surface of the FP cavity, thereby preventing the reflected light from the incident surface of the FP cavity from mixing with the signal light transmitted for the second time; the vertically polarized light transmitted from the exit surface of the FP cavity is reflected by the second reflector through the broadband Faraday isolator and transmitted to the first polarization beam splitter; the vertically polarized light is reflected by the first polarization beam splitter and transmitted to the same FP cavity again, and is filtered for the second time through the same FP cavity, thereby realizing multiple filtering using one FP cavity to improve the side mode suppression ratio; the vertically polarized light comb spectrum that passes through the FP cavity for the second time is restored to horizontally polarized light through the broadband Faraday rotator and the half-wave plate, so that the polarization states of the light comb spectrum that passes through the FP cavity for the first time and the light comb spectrum that passes through the FP cavity for the second time are perpendicular to each other through the broadband Faraday rotator and the half-wave plate, thereby distinguishing the light comb spectrum that passes through the FP cavity for the first time from the light comb spectrum that passes through the FP cavity for the second time, and the parallel polarized light comb spectrum that passes through the FP cavity for the second time is transmitted through the second polarization beam splitter and output as calibration light.

2. The optical comb frequency interval multiplication device according to claim 1, wherein: The FP cavity includes two cavity mirrors and a gasket. The first cavity mirror is a plano-concave reflector with one side flat and the other side concave, and the concave side faces inward; the second cavity mirror is a flat reflector with both sides flat, and there is a certain angle between the two planes to prevent the sub-cavity effect. The inner surfaces of the two plane reflectors are coated with a high-reflection film in the wavelength band, and the other plane reflector is coated with an anti-reflection film in the wavelength band; a gasket is arranged between the two cavity mirrors, and a vent is opened on the side of the gasket.

3. The optical comb frequency interval multiplication device according to claim 1, wherein: The vacuum chamber adopts a stainless steel structure, and the light entrance window and the light exit window of the vacuum chamber adopt quartz glass. Both sides of the light entrance window and the light exit window are plated with a broadband anti-reflection film.

4. The optical comb frequency interval multiplication device according to claim 1, wherein: The light entrance window and the light exit window are fixed and sealed to the vacuum chamber by using standard flanges.

5. The optical comb frequency interval multiplication device according to claim 1, wherein: The vacuum chamber is provided with an exhaust pipe, through which the vacuum chamber is evacuated to a vacuum better than 10 -5 Pa.

6. The optical comb frequency interval multiplication device according to claim 1, wherein: The broadband Faraday rotator and the broadband Faraday isolator are made of magneto-optical materials.

7. A method for implementing the optical comb frequency interval multiplication device according to claim 1, characterized in that: The implementation method comprises the following steps: 1) The optical frequency comb emits a broadband optical comb spectrum, and the polarization state of the optical comb spectrum is adjusted to horizontal polarization; 2) The broadband optical comb spectrum is split into multiple paths according to wavelength by an optical splitter, with one wavelength segment corresponding to one interval multiplication branch; 3) Horizontally polarized light enters the vacuum chamber through the corresponding light entrance window and is incident on the first polarization beam splitter. The horizontally polarized light passes through the first polarization beam splitter and is transmitted to the FP cavity of the corresponding wavelength band. 4) Frequency multiplication is performed by adjusting the FP cavity length to set the frequency interval, selecting the required frequency, i.e., the comb teeth. The frequency-multiplied optical comb spectrum is first transmitted to a broadband Faraday rotator and a half-wave plate. 5) The polarization state is converted from horizontal polarization to vertical polarization through a broadband Faraday rotator and a half-wave plate, and transmitted to the second polarization beam splitter; the vertically polarized light returning from the incident plane of the FP cavity is reflected by the first polarization beam splitter to the second reflector; 6) The vertically polarized light transmitted from the output surface of the FP cavity is reflected by the second polarization beam splitter and then reflected by the first reflector to the broadband Faraday isolator. The broadband Faraday isolator isolates the vertically polarized light returned from the incident surface of the FP cavity, preventing the vertically polarized light reflected from the incident surface of the FP cavity from returning to the output surface of the FP cavity, thereby preventing the reflected light from the incident surface of the FP cavity from mixing with the second transmitted signal light; 7) The vertically polarized light transmitted from the output surface of the FP cavity is reflected by the second reflector through the broadband Faraday isolator and transmitted to the first polarization beam splitter; 8) The vertically polarized light is reflected by the first polarization beam splitter and transmitted to the same FP cavity again, where it undergoes a second filtering, thus achieving multiple filtering using one FP cavity to improve the side mode suppression ratio. 9) The vertically polarized light comb spectrum that passes through the FP cavity for the second time passes through a broadband Faraday rotator and a half-wave plate and is restored to horizontally polarized light. The broadband Faraday rotator and the half-wave plate make the polarization states of the light comb spectrum that passes through the FP cavity for the first time and the light comb spectrum that passes through the FP cavity for the second time perpendicular to each other, thereby distinguishing the light comb spectrum that passes through the FP cavity for the first time from the light comb spectrum that passes through the FP cavity for the second time. The parallel polarized light comb spectrum that passes through the FP cavity for the second time passes through the second polarization beam splitter and is output as calibration light.

8. The implementation method according to claim 7, characterized in that: In step 3), the vacuum chamber is evacuated to a vacuum better than 10 -5 Pa.

9. The implementation method according to claim 7, wherein: In step 4), the FP cavity includes two cavity mirrors and a gasket, and the distance between the two cavity mirrors, that is, the cavity length of the FP cavity, is defined by the gasket, which sets the frequency multiplication multiple.

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